1. Field of the Invention
The present invention relates to apparatus for providing high voltage discharge to a patient, and more particularly to a defibrillation system in which a high voltage generating circuit charges a high voltage capacitor circuit using high voltage, and which is adapted to apply the high voltage charge to a patient's body by way of a paddle, upon closing an output switch.
2. Setting for the Invention
Conventional defibrillation systems often employ a high voltage capacitor circuit using a capacitor having metalfilm type electrodes and terminals having a tab structure with which lead wires can be inserted. Such capacitors tend to be bulky for use in high voltage capacitor circuits and present serious problems since the durable life of such capacitors are quite limited due to the fact that the lead wires thereof tend to fail when subjected to high stress typically accompanying normal operation, and due to the fact that the lead wires tend to deteriorate during the discharge of electrical current of large magnitude.
One prior art solution to the above-described problem has been to use metallized plastic film capacitors in the high voltage capacitor circuits of prior art defibrillation systems. In such systems, however, another significant problem arises regarding the performance of the metallized plastic film capacitors when being charged with high voltage. In particular, when metallized plastic film capacitors are subjected to high voltages such that they undergo dielectric breakdown, such capacitors are capable of preventing self-destruction during breakdown which is referred to as a "self-healing" action, and consequently are charged again with a high voltage which is lower than the prescribed voltage applied to the capacitor. In many cases, a metallized plastic film capacitor undergoing dielectric breakdown is unstable and is not in a condition suitable for active defibrillation.
In a metallized plastic film capacitor, the electrodes are composed of the positive layers and the lead wires extend from the metallic contact (i.e. metal sprayed) portions at both ends of the wound-up films. Although this arrangement makes it possible to reduce the parameter "tangent .delta.", it raises another problem. In particular, when dielectric breakdown occurs, short circuiting current may flow locally in the capacitor producing a loud noise similar to an explosion. Thus while metallized plastic film capacitors for use in high voltage capacitor circuits have advantages, the self-healing action and loud noise production during dielectric breakdown has made their use much less than desirable.
In view of the above-described shortcomings and drawbacks of metallized plastic film capacitors used in defibrillation systems, there is a great need for an effective solution to such accompanying problems.
Accordingly, it is the primary object of the present invention to solve such problems by providing a defibrillation system which includes a high voltage capacitor circuit using a metallized plastic film capacitor, and which is capable of automatically detecting the occurrance of dielectric breakdown of the high voltage capacitor and thereupon automatically ceasing the operation of the system.
Another object of the present invention is to provide a high voltage capacitor utilizing metallized plastic film capacitor elements, which is suitable for use in a defibrillation system.
According to the present invention, the defibrillation system comprises a high voltage generating circuit, a high voltage capacitor circuit, an output circuit, a charge abnormality detection circuit, a notifying means, and a switch circuit.
The high voltage capacitor circuit is adapted to be charged with the high voltage produced by the high voltage generating circuit, and includes a metallized plastic film capacitor. The output circuit includes a switch and is adapted to apply the high voltage to a paddle mounted on the body of a patient. The charge abnormality detection circuit detects either a sharp increase in charge current or a sharp drop in charge voltage which is caused by dielectric breakdown of the metallized plastic film capacitor. The notifying means responds to a detection signal produced by the charged abnormality detection circuit, and the switch circuit in response to the detection signal inhibits the feeding of the high voltage from the high voltage generating circuit to the high voltage capacitor circuit.
This arrangement makes possible the detection and notification of sharp drops in charge voltage and sharp increases in electrical currents associated with dielectric breakdown of the high voltage capacitor. Thus, even if a metallized plastic film capacitor is used as a high voltage capacitor of the defibrillation system, the present invention eliminates the problem arising as a result of the self-healing characteristics of the metallized plastic film capacitor, i.e. recharging thereof with an insufficiently high voltage and subsequent operation in and under unstable conditions.
Further, the metallized -plastic film capacitor of the present invention comprises a plurality of capacitor elements each of which have wound-up metallized plastic films and metallic contacts provided on the end surfaces of both sides thereof. Resistors each having a resistance at least equal to the internal resistance of each capacitor element per se, are connected to the metallic contact portions of the capacitor elements. By virtue of this arrangement, the high voltage capacitor for the defibrillation system hereof is made compact. In addition, since the capacitor is divided into a plurality of elements, the number of times the thin metal layers must be wound is reduced, thereby facilitating manufacture while improving the performance reliability of the capacitor.
Moreover, in the event of dielectric breakdown, short-circuiting discharge of capacitor elements are allowed to take place via the additional resistors, thereby avoiding any localized discharge and thereby reducing the level of noise associated with dielectric breakdown.